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Exploring the Free Energy Landscape of Solutes Embedded in Lipid Bilayers
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
2013 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 11, 1781-1787 p.Article in journal (Refereed) Published
Abstract [en]

Free energy calculations are vital for our understanding of biological processes on an atomistic scale and can offer insight to various mechanisms. However, in some cases, degrees of freedom (DOFs) orthogonal to the reaction coordinate have high energy barriers and/or long equilibration times, which prohibit proper sampling. Here we identify these orthogonal DOFs when studying the transfer of a solute from water to a model membrane. Important DOFs are identified in bulk liquids of different dielectric nature with metadynamics simulations and are used as reaction coordinates for the translocation process, resulting in two- and three-dimensional space of reaction coordinates. The results are in good agreement with experiments and elucidate the pitfalls of using one-dimensional reaction coordinates. The calculations performed here offer the most detailed free energy landscape of solutes embedded in lipid bilayers to date and show that free energy calculations can be used to study complex membrane translocation phenomena.

Place, publisher, year, edition, pages
2013. Vol. 4, no 11, 1781-1787 p.
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:su:diva-92267DOI: 10.1021/jz4007993ISI: 000320214600004OAI: oai:DiVA.org:su-92267DiVA: diva2:638066
Funder
Swedish Research Council, 621-2010-5005
Note

AuthorCount:2;

Available from: 2013-07-25 Created: 2013-07-25 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Computer Simulations of Heterogenous Biomembranes
Open this publication in new window or tab >>Computer Simulations of Heterogenous Biomembranes
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Molecular modeling has come a long way during the past decades and in the current thesis modeling of biological membranes is the focus. The main method of choice has been classical Molecular Dynamics simulations and for this technique a model Hamiltonian, or force field (FF), has been developed for lipids to be used for biological membranes. Further, ways of more accurately simulate the interactions between solutes and membranes have been investigated.

A FF coined Slipids was developed and validated against a range of experimental data (Papers I-III). Several structural properties such as area per lipid, scattering form factors and NMR order parameters obtained from the simulations are in good agreement with available experimental data. Further, the compatibility of Slipids with amino acid FFs was proven. This, together with the wide range of lipids that can be studied, makes Slipids an ideal candidate for large-scale studies of biologically relevant systems.

A solute's electron distribution is changed as it is transferred from water to a bilayer, a phenomena that cannot be fully captured with fixed-charge FFs.  In Paper IV we propose a scheme of implicitly including these effects with fixed-charge FFs in order to more realistically model water-membrane partitioning. The results are in good agreement with experiments in terms of free energies and further the differences between using this scheme and the more traditional approach were highlighted.

The free energy landscape (FEL) of solutes embedded in a model membrane is explored in Paper V. This was done using biased sampling methods with a reaction coordinate that included intramolecular degrees of freedom (DoF). These DoFs were identified in different bulk liquids and then used in studies with bilayers. The FELs describe the conformational changes necessary for the system to follow the lowest free energy path. Besides this, the pitfalls of using a one-dimensional reaction coordinate are highlighted.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2014. 82 p.
Keyword
Molecular simulation, force field development, biological membranes, free energy calculations, rational drug design, solute-membrane interactions
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-101297 (URN)978-91-7447-875-4 (ISBN)
Public defence
2014-04-04, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2014-03-13 Created: 2014-03-04 Last updated: 2015-01-21Bibliographically approved

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